Eye movements during fixation: implications to long-term viewing of small optical sources

Abstract

With the easy attainability of hand-held laser devices and burgeoning Light Emitting Diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. One concern is with formalizing the effect of eye movements on smearing energy from a small optical source over the retina. This experiment describes target motion over the retina as a result of eye movements during a deliberate fixation task. Volunteers fixated, with head and chin rest support, on a lmW HeNe laser source attenuated to 0.6pW/cm2, 5μW/cm2 or 10μW/cm2 comeal irradiance. The source was masked by a 25μm aperture yielding a small source subtending 0.1 minutes of arc visual angle. A dual Purkinje Eye-Tracker measured eye position every 243μs during each 100-second fixation trial. The data showed a non-uniform retinal energy distribution with an elliptical footprint. The major axis was, depending on condition, 3 to 4 times greater than the minor axis, and oriented along the temporal/nasal retinal axis. Increasing comeal irradiance from the picoWatt to the microWatt range resulted in a more circumscribed distribution of eye movements by a factor of 5. The dim light condition (0.6pW/cm2) yielded twice the dispersion of energy over the retina than did the bright light conditions (5μW/cm2, 10μW/cm2). Regardless of condition, eye movements did not provide the margin of safety afforded in the current laser safety standards.With the easy attainability of hand-held laser devices and burgeoning Light Emitting Diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. One concern is with formalizing the effect of eye movements on smearing energy from a small optical source over the retina. This experiment describes target motion over the retina as a result of eye movements during a deliberate fixation task. Volunteers fixated, with head and chin rest support, on a lmW HeNe laser source attenuated to 0.6pW/cm2, 5μW/cm2 or 10μW/cm2 comeal irradiance. The source was masked by a 25μm aperture yielding a small source subtending 0.1 minutes of arc visual angle. A dual Purkinje Eye-Tracker measured eye position every 243μs during each 100-second fixation trial. The data showed a non-uniform retinal energy distribution with an elliptical footprint. The major axis was, depending on condition, 3 to 4 times greater than the minor axis, and oriented along the temporal/nasal retinal axi...